1. Field of the Invention
The present invention relates to water-soluble and water-insoluble resins. The present invention also relates to synthetic resins and dispersions which contain the water-soluble and water-insoluble resins, and are free of low-molecular-weight emulsifiers. The synthetic resins can be used as binders in water-borne paints for printing processes. The present invention also relates to processes for their preparation and to their use.
2. Description of the Related Art
It is generally known that copolymers comprising monomers having acidic groups along with other monomers, are used as binders for aqueous printing inks and printing varnishes. In order to make these resins water-soluble or water-dispersible, they have usually been partially or completely neutralized with bases. In the aqueous phase, they exhibit a high absorption capacity for pigments and/or fillers and can also be used as polymer emulsifiers fillers emulsion polymerization to produce dispersions. These resin solutions and dispersions are then applied to substrates by conventional printing methods, frequently after the addition of water-soluble organic solvents which act as flow-improving or film-forming agents and, if also desired, after pigmenting. Examples of substrates are paper, wood, metal, sheets and/or other plastics.
EP-B 0,068,024 discloses, for example, acid synthetic resins based on styrene, .alpha.-methylstyrene and acrylic acid, which in principle are suitable for preparing water-borne inks and dispersions. A disadvantage of these commercially available products is their insufficient emulsifying power, which limits the absorption capacity for pigments and hydrophobic polymers.
EP-A 0,047,889 discloses polymer dispersions in which polar synthetic resins of low molecular weight and high acid number provide stabilization for relatively unpolar styrene/acrylate copolymers. When incorporated in printing varnishes and printing inks, resins of this type lead to insufficient rheological properties (viscosity/shearing stability) and their polarity results in insufficient pigment dispersing power and insufficient water resistance.
U.S. Patent No. 4,151,143 describes emulsifier-free acrylate dispersions obtained by grafting salts of acid synthetic resins with unsaturated monomers during emulsion polymerization. Since the acid synthetic resins used contain a relatively low molar proportion of carboxyl-containing monomers, the only dispersions obtainable by this method are those having a high proportion of partly water-dilutable acrylates and hydroxyacrylates, which leads to a reduction of the block and water resistance of the water-borne inks prepared using such dispersions.
U.S. Patent No. 4,465,803 discloses preparing water-soluble resins via solution polymerization and then using these resins for preparing dispersions via emulsion polymerization. The formation of emulsion addition polymers produces chemical bonds between reactive side groups of the resin and the emulsion addition polymer, as a result of which these dispersions are in reality no longer bi- or multimodal and thus, due to a lack in rheological properties, for example low shearing stability, are no longer suitable for use as binders for preparing varnishes and inks for printing processes.
Emulsifier-free polymer dispersions prepared by emulsion polymerization of unsaturated unpolar monomers in the presence of highly polar polyelectrolyte polymers also form the subject-matter of EP-A 0,511,520. However, for use as a binder base in aqueous printing inks, these systems are still in need of improvement with respect to their emulsifying capacity in emulsion polymerizations and with respect to their printing properties (see the comparative example which follows), since the insufficient emulsifying power of the polyelectrolyte polymers requires that the proportion of the polar polymers is at least 29% by weight of the total solids content. This leads to disadvantages, for example, during drying and with respect to the water and block resistance in aqueous systems in the printing sector.